N1 Set

[j14g]

On the freeware 752 panel there is an dial entitled N1 Set. What is N1 and what is its purpose?

Thanks

[Jason Downey GLE129]

I am not familiar with the freeware panel, however working on aircraft I can help you out with what is N1.

N1 is the rotational speed of the compressor section - Now in the world of a P&W engine, in which the 752 can come with, we use N1 to determine when fuel will be turned on during the engine start procedure.  N1 does not have a setting, rather it is hard and fast tied as a percent to how fast the compressor section is rotating.  For P&W engines the EPR (Engine Pressure Ratio) is the setting that can be change.

For the Pratt & Whitney PW2000 (and of course other jet engines) the start up numbers go a little like this.

starter button is pushed, N1 is your first number you see increasing until N2 has been picked up (N2 being speed of turbine section)

at 12% N1 fuel is turned on.

you will notice N1 increasing quickly as soon as you get light off.

at 55% the botton pops and the starter bleed air turns off engine continues under it's own power to spool

Now my numbers may be off a bit, but if I find my aircraft manuals I can go to more details about the PW2000 as the C17 uses the same engine, just with more redundancy.

Cheers

[Greg Mumbach GLE141]

I'm sure everything Jason said is right, but my answer is not going to sound much like his.

Once you start the engines, if you look at the engine gauges, you'll see that N1 is steady at around 20%. As you increase the throttle, you'll see N1 increase, along with increases in the other values displayed there.

The N1 set button you speak of is for setting the Autopilot N1 percentage. The autopilot, with autothrottle armed, can then be used to bring the engines up to the N1 percentage you set by pressing the N1 button on the Mode Control Panel.

To be honest though, I don't know when or why it would be used - I only know what it is.

Greg